SYMPOSIA PAPER Published: 01 January 1988
STP18748S

Glancing Incidence Absorption Measurements of Metal Mirrors

Source

Glancing incidence absorption measurements are performed on bare Cu, Mo, Au, Al, and Ag mirrors, and on Al and Ag mirrors with a protective dielectric overcoat. Data is obtained for angles of incidence from 0° to ⩾89°. Wavelengths studied are 0.5 μm and 10.6 μm at both s and p polarizations. The absorption is measured using a photoacoustic calorimetry technique in which the transducer is attached directly to the back of the test mirror. Absolute calibration of the absorption data is obtained by using a ratiometer to independently measure the absorption at near normal incidence.

The results are compared with the absorption predicted by Fresnel's equations for bare metals using values of n and k of the complex index of refraction measured by other sources. The absorption of a mirror at glancing incidence appears to be a sensitive function of its surface condition. New mirrors tend to agree with Fresnel's equations; while “old” mirrors have much higher absorption probably due to a layer of tarnish. The overcoated Al data deviates greatly from Fresnel's equations indicating that bare metal theory cannot be used and a thin film theory should be used instead. Representative results are given.

Author Information

Kimura, WD
Ford, DH
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Details
Developed by Committee: F01
Pages: 227–235
DOI: 10.1520/STP18748S
ISBN-EB: 978-0-8031-5031-7
ISBN-13: 978-0-8031-4479-8